Image-based feature detection using edge vectors

ABSTRACT

Techniques are provided in which a plurality of edges are detected within a digital image. An anchor point located along an edge of the plurality of edges is selected. An analysis grid associated with the anchor point is generated, the analysis grid including a plurality of cells. An anchor point normal vector comprising a normal vector of the edge at the anchor point is calculated. Edge pixel normal vectors comprising normal vectors of the edge at locations along the edge within the cells of the analysis grid are calculated. A histogram of similarity is generated for each of one or more cells of the analysis grid, each histogram of similarity being based on a similarity measure between each of the edge pixel normal vectors within a cell and the anchor point normal vector, and a descriptor is generated for the analysis grid based on the histograms of similarity.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/989,445 filed May 6, 2014. The entire content of that application ishereby incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates generally to image-based object recognition, andmore specifically to feature identification techniques for image-basedobject recognition.

BACKGROUND

Various feature detection algorithms are used for image-based objectrecognition. At the most basic level, feature detection algorithmsgenerate descriptors that provide a means to characterize, summarize andindex distinguishing features of an image (e.g., shapes, objects, etc.)for purposes of image-based object recognition, search and retrieval.One example of a feature detection algorithm for image-based objectrecognition is the Scale Invariant Feature Transform (SIFT) featuredetection algorithm, such as described in U.S. Pat. No. 6,711,293 toLowe. For example, the SIFT feature detection algorithm may be appliedto an image to generate descriptors for the numerous features within theimage.

Machine-based object recognition generally comprises two distinct steps.First, training images of known objects are analyzed using a featuredetection algorithm (e.g., a SIFT feature detection algorithm), whichgenerates descriptors associated with features in the image data.Descriptors associated with many different objects can be packaged as arecognition library or database for deployment on a recognition device(e.g., a smartphone). Second, the recognition device captures a new“query” image of an object. The device applies the same featuredetection algorithm to the query image, thereby generating query imagedescriptors. The device then compares the query image descriptors to thetraining image descriptors in the recognition library. If there aresufficient matches, typically nearest neighbor matches, then the queryimage is considered to contain a representation of at least one of theknown objects.

SUMMARY

The various feature detection algorithms are generally based ondifferent underlying philosophies. As such, certain descriptors may beparticularly useful for certain object recognition situations. Forexample, some descriptors are generally efficient for describingfeatures that track across frames of video data (e.g., FAST cornersdescriptors), while other descriptors are generally efficient fordescribing various object geometries. An ideal descriptor would beuseful for multiple image-based object recognition purposes.

Many image recognition technologies have difficulty differentiatingbetween texture-rich objects (e.g., an action figure toy or brick walls)and texture-poor objects (e.g., a solid-color field logo, metal slabs orsheets of glass) in a single image. For example, edge feature gradientscan change substantially, e.g., from one video frame to another, suchthat absolute information (e.g., information obtained at only one pointalong the edge) may fail to account for relative information, e.g.,information regarding a relationship between one part of an edge andanother part of the edge. Rather than requiring multiple types ofdescriptors for object recognition, a single type of descriptor that canprovide efficient image-based object recognition capabilities fortexture-rich as well as texture-poor images would be advantageous.

Methods, systems and articles of manufacture for generating anedge-based feature descriptor for a digital image are described herein.The various embodiments can provide efficient image-based objectrecognition capabilities for texture-rich images as well as texture-poorimages. In an embodiment, a plurality of edges are detected within adigital image. The digital image may be one of a video frame of a videostream and a rendered image. The plurality of edges may be detectedbased on one of tensor voting and a Canny edge detection algorithm. Ananchor point located along an edge of the plurality of edges isselected. The anchor point may be a feature corresponding to at leastone of a scale-invariant feature transform (SIFT), Fast Retina Keypoint(FREAK), Histograms of Oriented Gradient (HOG), Speeded Up RobustFeatures (SURF), DAISY, Binary Robust Invariant Scalable Keypoints(BRISK), FAST, Binary Robust Independent Elementary Features (BRIEF),Harris Corners, Edges, Gradient Location and Orientation Histogram(GLOH), Energy of image Gradient (EOG) or Transform Invariant Low-rankTextures (TILT) feature. An analysis grid associated with the anchorpoint is generated, the analysis grid including a plurality of cells. Ananalysis grid associated with the anchor point may have a geometriccenter at the anchor point, and may include one of a polar grid, aradial polar grid or a rectilinear grid. An anchor point normal vectorcomprising a normal vector of the edge at the anchor point iscalculated. The anchor point normal vector may be one of a Harris matrixeigenvector or a geometric normal vector orthogonal to the edge at apixel coordinate of the anchor point. One or more edge pixel normalvectors comprising normal vectors of the edge at one or more locationsalong the edge within the cells of the analysis grid are calculated. Theedge pixel normal vectors may be one of a Harris matrix eigenvector or ageometric normal vector orthogonal to the edge at a pixel coordinate. Ahistogram of similarity is generated for each of one or more cells ofthe analysis grid, each histogram of similarity being based on asimilarity measure between each of the edge pixel normal vectors withina cell and the anchor point normal vector, and a descriptor is generatedfor the analysis grid based on the histograms of similarity. Generatingthe descriptor may include concatenating data from the histograms ofsimilarity for one or more of the cells of the analysis grid. Animage-based object recognition search may be facilitated using thedescriptor for the analysis grid.

In some embodiments, at least one degenerate edge may be eliminated fromthe plurality of edges.

In some embodiments, the digital image may be scaled by a scalingfactor, and the plurality of edges may be detected within the scaleddigital image. In some embodiments, the scaling factor may be at least1.5. In some embodiments, the scaling factor may be at least 2.0.

In some embodiments, the anchor point may comprise a detected corner ofthe edge.

In some embodiments, the analysis grid may be oriented based on theanchor point normal vector.

In some embodiments, the analysis grid may comprise at least five cells.In some embodiments, the analysis grid may comprise at least nine cells.

In some embodiments, the similarity measure may be based on one of arelative angle or a dot product between each of the edge pixel normalvectors within a cell and the anchor point normal vector.

In some embodiments, the similarity measure may be based on a comparisonbetween a magnitude of each of the edge pixel normal vectors within acell and a magnitude of the anchor point normal vector. The magnitude ofeach of the edge pixel normal vectors within a cell and the magnitude ofthe anchor point normal vector may be based on a non-orientation basedmeasurement.

In some embodiments, the similarity measure may be based on one or moreweighting factors. The one or more weighting factors may be based on oneof a Euclidean distance and a Gaussian weight.

In some embodiments, each histogram of similarity may include aplurality of bins. In some embodiments, each histogram of similarity mayinclude at least four bins or at least 16 bins. Bin values for theplurality of bins may be normalized based on a maximum bin value, andmay range between 0 and 255.

In some embodiments, a concatenation order may be determined for thedata from the histograms of similarity. The concatenation order may bebased on an orientation of the cells of the analysis grid relative tothe anchor point normal vector.

In some embodiments, the descriptor may be a multi-dimensional vectorhaving a number of dimensions based on a number of cells in the analysisgrid. In some embodiments, the descriptor may be a multi-dimensionalvector having a number of dimensions based on a total number of bins inthe histograms of similarity for the analysis grid.

In some embodiments, a plurality of anchor points located along the edgemay be selected, wherein the anchor points are equidistant along theedge with respect to each other. In some embodiments, a plurality ofanchor points located along the edge may be selected in accordance withat least one of a determined distribution of analysis grids along theedge, a determined amount of analysis grids per unit area, a determinedamount of analysis grids per unit volume, a selected object model, ordepth field information associated with the digital image.

Various objects, features, aspects and advantages of the inventivesubject matter will become more apparent from the followingspecification, along with the accompanying drawings in which likenumerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a digital image in accordance with anembodiment;

FIG. 2 illustrates an example of a plurality of edges detected within adigital image in accordance with an embodiment;

FIG. 3A illustrates an example of an anchor point selected in accordancewith an embodiment;

FIG. 3B illustrates an example of an analysis grid generated inassociation with an anchor point in accordance with an embodiment;

FIG. 4 illustrates an example of edge pixel normal vectors calculatedwithin cells of an analysis grid in accordance with an embodiment;

FIG. 5 illustrates an example of a histogram of similarity generated fora cell of an analysis grid in accordance with an embodiment;

FIG. 6 illustrates an example of a descriptor generated for an analysisgrid based on histograms of similarity in accordance with an embodiment;

FIG. 7 illustrates a block diagram of a system for generating anedge-based feature descriptor for a digital image in accordance with anembodiment;

FIG. 8 illustrates a flow diagram of example operations for generatingan edge-based feature descriptor for a digital image in accordance withan embodiment;

FIG. 9 illustrates an example of generating an edge-based featuredescriptor for an image of a texture-poor object in accordance with anembodiment;

FIG. 10 illustrates an example of image-based object recognition for animage of a texture-poor object in accordance with an embodiment;

FIG. 11 illustrates an example of image-based object recognition for animage of a texture-rich object in accordance with an embodiment;

FIG. 12 illustrates an example of image-based object recognition for animage of a texture-poor three-dimensional object in accordance with anembodiment; and

FIG. 13 illustrates a block diagram of a distributed computer systemthat can be used for implementing one or more aspects of the variousembodiments.

While the invention is described with reference to the above drawings,the drawings are intended to be illustrative, and other embodiments areconsistent with the spirit, and within the scope, of the invention.

DETAILED DESCRIPTION

The various embodiments now will be described more fully hereinafterwith reference to the accompanying drawings, which form a part hereof,and which show, by way of illustration, specific examples of practicingthe embodiments. This specification may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this specification will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Amongother things, this specification may be embodied as methods or devices.Accordingly, any of the various embodiments herein may take the form ofan entirely hardware embodiment, an entirely software embodiment or anembodiment combining software and hardware aspects. The followingspecification is, therefore, not to be taken in a limiting sense.

Throughout the specification and claims, the following terms take themeanings explicitly associated herein, unless the context clearlydictates otherwise:

The phrase “in one embodiment” as used herein does not necessarily referto the same embodiment, though it may. Thus, as described below, variousembodiments of the invention may be readily combined, without departingfrom the scope or spirit of the invention.

As used herein, the term “or” is an inclusive “or” operator, and isequivalent to the term “and/or,” unless the context clearly dictatesotherwise.

The term “based on” is not exclusive and allows for being based onadditional factors not described, unless the context clearly dictatesotherwise.

As used herein, and unless the context dictates otherwise, the term“coupled to” is intended to include both direct coupling (in which twoelements that are coupled to each other contact each other) and indirectcoupling (in which at least one additional element is located betweenthe two elements). Therefore, the terms “coupled to” and “coupled with”are used synonymously. Within the context of a networked environmentwhere two or more components or devices are able to exchange data, theterms “coupled to” and “coupled with” are also used to mean“communicatively coupled with”, possibly via one or more intermediarydevices.

In addition, throughout the specification, the meaning of “a,” “an,” and“the” includes plural references, and the meaning of “in” includes “in”and “on.”

Although some of the various embodiments presented herein constitute asingle combination of inventive elements, it should be appreciated thatthe inventive subject matter is considered to include all possiblecombinations of the disclosed elements. As such, if one embodimentcomprises elements A, B, and C, and another embodiment compriseselements B and D, then the inventive subject matter is also consideredto include other remaining combinations of A, B, C, or D, even if notexplicitly discussed herein.

As used in the description herein and throughout the claims that follow,when a system, engine, server, device, module, or other computingelement is described as being configured to perform or execute functionson data in a memory, the meaning of “configured to” or “programmed to”is defined as one or more processors or cores of the computing elementbeing programmed by a set of software instructions stored in the memoryof the computing element to execute the set of functions on target dataor data objects stored in the memory.

It should be noted that any language directed to a computer should beread to include any suitable combination of computing devices, includingservers, interfaces, systems, databases, agents, peers, engines,controllers, modules, or other types of computing device structuresoperating individually or collectively. One should appreciate thecomputing devices comprise a processor configured to execute softwareinstructions stored on a tangible, non-transitory computer readablestorage medium (e.g., hard drive, FPGA, PLA, solid state drive, RAM,flash, ROM, etc.). The software instructions configure or program thecomputing device to provide the roles, responsibilities, or otherfunctionality as discussed below with respect to the disclosedapparatus. Further, the disclosed technologies can be embodied as acomputer program product that includes a non-transitory computerreadable medium storing the software instructions that causes aprocessor to execute the disclosed steps associated with implementationsof computer-based algorithms, processes, methods, or other instructions.In some embodiments, the various servers, systems, databases, orinterfaces exchange data using standardized protocols or algorithms,possibly based on HTTP, HTTPS, AES, public-private key exchanges, webservice APIs, known financial transaction protocols, or other electronicinformation exchanging methods. Data exchanges among devices can beconducted over a packet-switched network, the Internet, LAN, WAN, VPN,or other type of packet switched network; a circuit switched network;cell switched network; or other type of network.

The focus of the disclosed inventive subject matter is to enableconstruction or configuration of a computing device to operate on vastquantities of digital data, beyond the capabilities of a human.Although, in some embodiments, the digital data represents images ofobjects, it should be appreciated that the digital data is arepresentation of the objects, not necessarily the objects themselves.By instantiation of such digital models or digital images in the memoryof the computing devices, the computing devices are able to manage thedigital data or models in a manner that could provide utility to a userof the computing device that the user would lack without such a tool.Thus, the disclosed devices are able to process such digital data in amore efficient manner according to the disclosed techniques.

One should appreciate that the disclosed techniques provide manyadvantageous technical effects including improving the scope, accuracy,compactness, efficiency and speed of digital image-based objectrecognition and retrieval technologies. It should also be appreciatedthat the following specification is not intended as an extensiveoverview, and as such, concepts may be simplified in the interests ofclarity and brevity.

In accordance with the various embodiments, object instance retrieval,referred to herein in the context of image retrieval, image recognitionand/or image-based object recognition, involves systems and methods offeature detection for an image dataset (referred to herein individuallyas “images” or “digital images”) in response to a given query image.Image recognition is made possible through the use of descriptors thatcharacterize, summarize and index distinguishing features of an image.Large-scale image recognition can involve multiple servers running inparallel and image datasets of 10 million or more images per server(relative to image datasets of about 1 million images per server formedium-scale image recognition). However, due to the storagerequirements for the descriptors that correspond to large imagedatasets, there is often a tradeoff between the memory footprint ofimage descriptors and image retrieval performance as measured by, forexample, mean average precision (mAP). Therefore, the use of fewer imagedescriptors to characterize images is preferable to perform imagerecognition on a large scale.

FIG. 1 illustrates an example of a digital image in accordance with anembodiment. In FIG. 1, digital image 100 illustrates an image or digitalrepresentation of one or more objects. Digital image 100 may be one ofan infrared-filtered image, an x-ray image, a 360-degree view image, asynthetic image, a machine-view image, a frame of video data, agraphical rendering, a three-dimensional perspective-view of one or moreobjects, or other type of digital image. Digital image 100 also mayillustrate a digital image that has been scaled, e.g., up-scaled ordown-scaled, by a scaling factor. The one or more objects within digitalimage 100 may include any combination of texture-rich, medium texture ortexture-poor objects including, for example, medical information,people, animals, plants, toys, buildings, products, bar codes, printedmatter, or other types of objects.

In some embodiments, digital image 100 may be a portion of an image or aportion of a larger image structure (e.g., a cut out of an image, animage of a person's face extracted from a photograph of a group ofpeople posted on a social media website, or a frame of a videosequence). For example, digital image 100 may be obtained by capturing avideo frame of a video stream, such as via an image capture device orfrom a broadcast (e.g., television, movie, etc.).

Descriptors can be vectors that correspond to one or moredistinguishable features of an image (e.g., shapes, objects, etc.).There are various methods for detecting image features and generatingdescriptors. For example, the scale-invariant feature transform (SIFT)is a currently popular image recognition algorithm used to detect anddescribe features of images. SIFT descriptors are 128-dimensions inorder to be highly distinctive (i.e., distinguishable for matchingpurposes) and at least partially tolerant to variations such asillumination, three-dimensional (3D) viewpoint, etc. For example, onereference related to generating SIFT descriptors is D. Lowe,“Distinctive Image Features from Scale-Invariant Keypoints”,International Journal of Computer Vision 60 (2), pages 91-110 (2004). Inaddition to SIFT descriptors, other alternative descriptors include FastRetina Keypoint (FREAK) descriptors, Histograms of Oriented Gradient(HOG) descriptors, Speeded Up Robust Features (SURF) descriptors, DAISYdescriptors, Binary Robust Invariant Scalable Keypoints (BRISK)descriptors, FAST descriptors, Binary Robust Independent ElementaryFeatures (BRIEF) descriptors, Harris Corners descriptors, Edgesdescriptors, Gradient Location and Orientation Histogram (GLOH)descriptors, Energy of image Gradient (EOG) descriptors and TransformInvariant Low-rank Textures (TILT) descriptors. Typically, each image ofan image dataset may include hundreds or thousands of featuresrepresented by descriptors. Therefore, practical system constraints willoften require methods to both compress the amount of descriptors used todescribe an image dataset, and to reduce in size the memory required tostore the information contained in descriptors.

Edge-based feature descriptors may be advantageous for providingefficient image-based object recognition capabilities for various (e.g.,texture-rich, texture-poor) digital images. For example, an edgedetection algorithm may be applied to detect a plurality of edges withina digital image, such as digital image 100. An anchor point locatedalong an edge of the plurality of edges may be selected, and an analysisgrid including a plurality of cells associated with the anchor point maybe generated. An edge-based feature descriptor for the analysis grid maythen be determined based on histograms of similarity between edgeinformation at an anchor point, and edge information within the cells ofthe analysis grid associated with the anchor point. As such, a libraryof edge-based feature descriptors for digital image 100 may beassociated with known objects (e.g., people, buildings, vehicles, barcodes, printed media, etc.) to facilitate an image-based objectrecognition search.

FIG. 2 illustrates an example of a plurality of edges detected within adigital image in accordance with an embodiment of the disclosed subjectmatter. As shown in FIG. 2, digital image 200 may include a plurality ofedges, e.g., edges 202. The plurality of edges 202 may be detectedwithin digital image 200 based on various edge detection techniques. Ingeneral, a goal of edge detection is to identify locations at which animage has discontinuities that are determined to be significant.

In an exemplary embodiment, the plurality of edges 202 may be detectedby applying tensor voting concepts to digital image 200, e.g., to groupedge pixels (i.e., edgels) to an edge. Tensor voting is a technique forextracting and grouping structures from a cloud of points, such aswithin a digital image. In general, tensor voting includes estimatingsaliency measurements of a likelihood that a point (e.g., an imagepixel) lies on a surface, curve, or junction, or whether it is noisy,and is based on the propagation and aggregation of the most likelynormal(s) encoded by means of tensors. In a first stage, a tensor isinitialized at every point in the cloud either with a first estimationof the normal, or with a ball-shaped tensor if predetermined informationis not available. Next, every tensor is decomposed into threecomponents: a stick, a plate and a ball. Every component casts votes,which are tensors that encode the most likely direction(s) of the normalat a neighboring point by taking into account the information encoded bythe voter in that component. The votes are then summed and analyzed toestimate surface, curve and junction measurements at every point. Pointswith low saliency are assumed to be noisy.

In another exemplary embodiment, the plurality of edges 202 may bedetected by applying a Canny edge detection algorithm to digital image200. In general, a Canny edge detection algorithm includes applying aGaussian filter to smooth an image in order to remove noise, determiningintensity gradients of the image, applying non-maximum suppression(e.g., an edge-thinning technique) to eliminate spurious responses toedge detection, applying a double threshold to determine potentialedges, and tracking edges by hysteresis to finalize the edge detectionby, for example, eliminating weak edges that are not connected to strongedges. As such, in various embodiments, a Canny edge detection algorithmmay be used to detect edge pixels, while tensor voting concepts may beused to group edge pixels to an edge.

In some embodiments, a plurality of edges may be detected within digitalimage 200 by connecting one or more edgelets together to form an edge.For example, an edgelet may be represented by a circular arc having aradius of curvature, and each edgelet may include edgels (e.g., pixelsin the image) that may be determined to be located along an edge.

In some embodiments, edge detection may include techniques that providefor scale invariance. For example, digital image 200 may be scaled by ascaling factor to extract sets of edges at each of a plurality ofscales. Thus, digital image 200 may be down-scaled multiple times (e.g.,by a factor of two) until a practical lower limit is reached. Forexample, scaling factors may include 1.5, 1.75, 2.25, 2.5, or otherfactors. In an embodiment, the scaling factor may preferably be at least1.5, or at least 2.0, to provide for generally sufficient scaleinvariance and for greater computational efficiency relative to otherscaling factors.

One skilled in the art will appreciate that while the edge detectiontechniques described herein are exemplary, various other edge detectiontechniques may be applied to determine a plurality of edges within adigital image. For example, exemplary systems and methods for edgedetection are described in U.S. patent application Ser. No. 14/623,341,entitled “Edge-Based Recognition, Systems and Methods”, filed on Feb.16, 2015, which is incorporated in its entirety by reference herein. Oneskilled in the art will appreciate that certain edges, e.g., degenerateedge 208, within in digital image 200 may be eliminated from theplurality of edges to reduce noise. For example, singleton lines (e.g.,circular arcs with very low curvature and having larger radii) that lackother edges close by may be eliminated from the plurality of edges dueto, e.g., their lack of resolving power for an image-based objectrecognition search.

FIG. 3A illustrates an example of an anchor point selected in accordancewith an embodiment. In FIG. 3A, an anchor point 300 along edge 302 isselected within a digital image (e.g., digital image 200). For example,edge 302 may be one edge of a plurality of edges detected using an edgedetection technique, such as described above. Anchor point 300 may beselected to be at any location (e.g., a pixel location) along edge 302.In an embodiment, anchor point 300 may be selected by utilizing afeature detection algorithm. For example, in some embodiments anchorpoint 300 may be a feature corresponding to at least one of ascale-invariant feature transform (SIFT), Fast Retina Keypoint (FREAK),Histograms of Oriented Gradient (HOG), Speeded Up Robust Features(SURF), DAISY, Binary Robust Invariant Scalable Keypoints (BRISK), FAST,Binary Robust Independent Elementary Features (BRIEF), Harris Corners,Edges, Gradient Location and Orientation Histogram (GLOH), Energy ofimage Gradient (EOG) or Transform Invariant Low-rank Textures (TILT)feature. Further, in some embodiments anchor point 300 may be selectedto be located at a particular point of interest along edge 302. Forexample, anchor point 300 may be located at a detected corner of edge302, or at another type of detected feature (e.g., an inflection point,a change in curvature of the edge above a threshold, etc.) along edge302. In some embodiments, features such as detected corners may be ofparticular interest because they may be tracked during a real-time orframe-by-frame analysis of video streaming data. Also, features locatedat detected corners of an edge may include texture information relatedto the image data. As such, one skilled in the art will appreciate thatan anchor point may be selected to be located at any point that issubstantially along a detected edge, or within a threshold distance froma detected edge.

It should be appreciated that although FIG. 3A illustrates only oneanchor point, a plurality of anchor points may be selected along edge302, e.g., to generate a plurality of descriptors for an image. In someembodiments, a plurality of anchor points located along an edge may beselected in accordance with at least one of a determined distribution ofanalysis grids along the edge, a determined amount of analysis grids perunit area, a determined amount of analysis grids (as described below)per unit volume, a selected object model, or depth field informationassociated with the digital image. For example, a plurality of anchorpoints located along edge 302 may be selected as being equidistant alongthe edge with respect to each other.

In an embodiment, an anchor point normal vector 304 comprising a normalvector of the edge at the anchor point may be calculated. For example,anchor point normal vector 304 illustrates a normal vector, such as aunit normal vector, that includes information associated with edge 302at anchor point 300. In an embodiment, anchor point normal vector 304may be one of a Harris matrix eigenvector or a geometric normal vectororthogonal to the edge at a pixel coordinate of the anchor point. Forexample, anchor point normal vector 304 may correspond to a Harrismatrix eigenvector that points from high brightness to low brightness,wherein the Harris matrix may be determined to have an average windowsize of, for example, nine pixels (i.e., the pixel coordinate of theanchor point and eight neighboring pixels) to reduce noise whilemaintaining computational efficiency. In another example, anchor pointnormal vector 304 may be a geometric normal vector that is substantiallyorthogonal to edge 302 at anchor point 300 (e.g., at a pixel coordinateassociated with anchor point 300). For example, a geometric normalvector at anchor point 300 may be calculated based on radius ofcurvature information associated with edge 302, or based on radius ofcurvature information associated with edgelets or edgels of edge 302, ifsuch information is available.

FIG. 3B illustrates an example of an analysis grid generated inassociation with an anchor point in accordance with an embodiment. Ingeneral, an analysis grid represents an artificial construct that may beused to analyze a curve in an area around an associated anchor point.For example, in FIG. 3B analysis grid 310 is associated with anchorpoint 300, while analysis grid 340 is associated with anchor point 330.In various embodiments, an analysis grid may be one of a polar grid, aradial polar grid or a rectilinear grid. For example, analysis grid 310and analysis grid 340 are polar grids, or radially polar grids. In someembodiments, depending on a number of features identified on an edge,analysis grids may be evenly distributed for at least some of multipleanchor points along the edge. For example, a plurality of anchor pointsmay be distributed such that they are equidistant along an edge fromeach other. The analysis grids corresponding to the plurality of anchorpoints may then be either overlapping or generated such that they arerestricted from overlapping (such as shown). Further, the anchor pointsand corresponding analysis grids may be distributed evenly based on adesired number of analysis grids per unit area within a digital image, adesired number of analysis grids per unit volume within a 3D space(e.g., within a perspective view of a 3D object model), based on apredetermined (i.e., a priori known) object model or based on depth offield information derived from image data.

In an embodiment, an analysis grid may include a plurality of cells(i.e., divisions). For example, exemplary analysis grid 310 includesfive cells (i.e., center cell 312 surrounded by arcuate cells 314, 316,318 and 320), while analysis grid 340, also exemplary, includes ninecells (i.e., center cell 342, arcuate cells 344, 346, 348 and 350 in aninner shell, and arcuate cells 352, 354, 356 and 358 in an outer shell).It should be appreciated that an analysis grid may include any number ofcells or divisions. As such, while an analysis grid including at leastfive cells, or including at least nine cells, is exemplary, variousarrangements, configurations and numbers of cells are possible.

In some embodiments, an analysis grid, including the number of cells oftherein, may be scaled based on one or more characteristics of anassociated anchor point. For example, an analysis grid may be scaledbased on a determined size of an associated anchor point, wherein thesize of the associated anchor point may relate to one or morecharacteristics of a feature (e.g., a SIFT feature) associated with theanchor point. Therefore, analysis grids may be scaled proportionallywith respect to their associated anchor points (and with respect to eachother), such that the analysis grids within a digital image may bescale-invariant, e.g., with respect to different scaled versions of thedigital image.

In an embodiment, an analysis grid may be oriented based on an anchorpoint normal vector. For example, analysis grid 310 and analysis grid340 are oriented based on the anchor point normal vectors for anchorpoint 300 and anchor point 330, respectively. As a result, analysis grid310 and analysis grid 340 may be rotationally invariant with respect tothe anchor point normal vectors anchor point 300 and anchor point 330,respectively. Similarly, an analysis grid may have a geometric center ata location associated with an anchor point (e.g., a geometric center ata pixel coordinate associated with an anchor point).

FIG. 4 illustrates an example of edge pixel normal vectors calculatedwithin cells of an analysis grid in accordance with an embodiment. FIG.4 includes a close-up representation of a portion of a radial polaranalysis grid 400, which is generally similar to analysis grid 310 inFIG. 3B. For example, analysis grid 400 is oriented based on anchorpoint normal vector 402 to provide orientation invariance. For example,such an alignment may be chosen to allow for a consistent representationof the analysis grid from feature-to-feature as well as to provide for aconsistent method of calculating descriptors based on the embodimentsherein. Analysis grid 400 includes center cell 404, and arcuate cells406-410. Other arcuate cells of analysis grid 400 are not shown for thesake of clarity. Further, the ordering of the cells within analysis grid400, including center cell 404 (i.e., surrounding anchor point normalvector 402) and arcuate cells 406, 408 and 410 in an outer shell runningin an angular arc of 0 to 90 degrees relative to anchor point normalvector 402, is one possible method of ordering cells in an analysisgrid. However, the cell sizes (e.g., the radial distances in pixels) maybe adjusted. As such, all practical cell sizes, configurations,orientations, or orderings may be employed in the various embodiments.

Edges 420 and 430 pass through analysis grid 400. Specifically, edge 420passes through arcuate cell 406 and center cell 404, while edge 430passes through arcuate cell 408 and center cell 404. It should be notedthat edges that pass through more than one cell may increase theresolving power of a feature descriptor generated based on theembodiments herein. Further, the paths of edge 420 and edge 430, e.g.,such as may be determined based on an edge detection technique, includea plurality of pixels 440 and 450, respectively, within analysis grid400. For the sake of clarity only a small number of pixels are shown.

In an embodiment, edge information (e.g., curvature information fromedgelets or a Harris matrix) may be used to calculate an edge pixelnormal vector for each pixel that is located on an edge within the cellsof an analysis grid, e.g., analysis grid 400. For example, an edge pixelnormal vector 460 may be calculated for each edge pixel 450 along edge420, wherein each of the edge pixel normal vectors 460 may be one of aHarris matrix eigenvector or a geometric normal vector orthogonal toedge 420 at a pixel coordinate.

FIG. 5 illustrates an example of a histogram of similarity generated fora cell of an analysis grid in accordance with an embodiment. A histogramof similarity 500 may be generated for each of one or more cells of ananalysis grid. For example, five-cell analysis grid 310 in FIG. 3B mayhave a five-cell histogram of similarity (or a histogram of similaritywith fewer cells), while nine-cell analysis grid 340 may have anine-cell histogram of similarity (or a histogram of similarity withfewer cells).

In an embodiment, histogram of similarity 500 is based on a similaritymeasure between each of the edge pixel normal vectors within a cell andthe anchor point normal vector. For example, the similarity measure maybe a relative angle, θ (as shown), between an anchor point normal vector502 and each of the edge pixel normal vectors, e.g., edge pixel normalvector 504. Thus, the similarity measure may be a relative angle rangingbetween 0 degrees and 360 degrees (i.e., 0 to 2π radians). In anotherexample, the similarity measure may be based on a cos(θ) or dot productbetween the anchor point normal vector and each of the edge pixel normalvectors. Thus, the similarity measure may be a dot product value rangingbetween −1 and 1. In preferred embodiments, the similarity measure willallow for a uniform distribution of values in a histogram of similarityin order to represent how similar the anchor point normal vector andeach of the edge pixel normal vectors are relative to each other. Assuch, in preferred embodiments a histogram of similarity will representinformation regarding the relative similarity between the anchor pointnormal vector and each of the edge pixel normal vectors, rather thanabsolute information (e.g., at pixel coordinate).

In some embodiments, the similarity measure may be based on additionalvector information, such as a comparison between a magnitude of each ofthe edge pixel normal vectors within a cell and a magnitude of theanchor point normal vector. For example, the magnitude of each of theedge pixel normal vectors within a cell and the magnitude of the anchorpoint normal vector may be based on a non-orientation based measurement.As such, rather than having a normalized magnitude of one, each of theedge pixel normal vectors within a cell and the anchor point normalvector may include a magnitude based on, for example, various propertiesof the edge at a pixel location, including edge curvature information,color (e.g., relative RGB intensity) information, etc. Therefore, thesimilarity measure may represent a relative comparison of magnitudes,e.g., a log value of a ratio of vector magnitudes. For example, a logvalue of 0 (i.e., log(1)) may indicate vectors having identicalmagnitudes while positive or negative values may indicate differences inrelative vector magnitudes.

In some embodiments, the similarity measure may be based on one or moreweighting factors. For example, the similarity measure may be adjustedbased on a Euclidean distance (d) between the anchor point and each ofthe edge pixels. In another example, the similarity measure may beadjusted based on a weighting factor that may include a factor of1/Euclidean distance (d) or a Gaussian weight. One skilled in the artwill appreciate that a variety of similarity measures may be employed.Therefore, the examples of similarity measures described herein, whileexemplary, should not be construed as being limiting for the variousembodiments.

A histogram of similarity may include a plurality of bins that areevenly spaced with respect to angular range. In an embodiment, ahistogram of similarity preferably includes at least four bins, and morepreferably at least 16 bins. However, it will be appreciated that ahistogram of similarity may comprise any practical number of bins. Forexample, histogram of similarity 500 includes 16 bins evenly spaced(e.g., every 22.5 degrees) to cover a full range of possible anglesbetween 0 degrees and 360 degrees. It should be appreciated that theamount and spacing of bins within a histogram of similarity may beadjusted to account for various factors, including resolving powerduring an image-based object recognition search and image-based objectrecognition search time.

In an embodiment, histogram of similarity bin values may be normalizedso that they do not exceed a determined maximum value. For example, binvalues may range between 0 and 255 for the values to be easilyrepresented in a computer memory. As such, a bin value between 0 and 255may be represented by a single byte, meaning that a 16 bin histogram ofsimilarity may be represented by 16 bytes.

FIG. 6 illustrates an example of a descriptor generated for an analysisgrid based on histograms of similarity in accordance with an embodiment.For example, for a five-cell analysis grid (e.g., analysis grid 310 inFIG. 3B), grid descriptor 600 may be based on histogram of similarityinformation from each of the five cells. If each the histograms ofsimilarity include 16 bins, then grid descriptor 600 would have 80dimensions (i.e., 5*16). Likewise, for a nine-cell analysis grid (e.g.,analysis grid 340 in FIG. 3B) where each cell's histogram of similarityincludes 16 bins, the grid descriptor would have 144 dimensions (i.e.,16*9).

In an embodiment, grid descriptor 600 may be generated by concatenatingdata from the histograms of similarity for one or more of the cells ofan analysis grid. As such, generating a grid descriptor may includedetermining a concatenation order for the data from the histograms ofsimilarity. In some embodiments, the concatenation order may be based onan orientation of the cells of the analysis grid relative to the anchorpoint normal vector. For example, a concatenation of data from thehistograms of similarity associated with analysis grid 310 may beordered based on the relative orientation of the cells to the anchorpoint normal vector, such that the descriptor includes data from centercell 312 first, followed by data from cell 314, cell 316, cell 318 andcell 320. It will be appreciated that the data from the histograms ofsimilarity may be arranged for concatenation in any of a variety ways,including, for example, ways that prioritize or deemphasize certain data(e.g., based on a principal component analysis (PCA) or otherdimensional reduction technique). For example, a descriptor may beordered such that certain of the data (e.g., histogram of similaritydata associated with cell 320 in analysis grid 310) appears near thebeginning of the descriptor, e.g., to maximize the resolving power ofthe data within the various histograms of similarity with respect to animage-based object recognition search, and/or to increase the robustnessof the data with respect to certain affine transforms of an associateddigital image.

FIG. 7 illustrates a block diagram of a system for generating anedge-based feature descriptor for a digital image in accordance with anembodiment. In block diagram 700, elements for generating edge-basedfeature descriptors include a feature detector 710, image capture device720, a persistent storage device 730 and a main memory device 740.However, it should be noted that the elements in FIG. 7, and the variousfunctions attributed to each of the elements, while exemplary, aredescribed as such solely for the purposes of ease of understanding. Oneskilled in the art will appreciate that one or more of the functionsascribed to the various elements may be performed by any one of theother elements, and/or by an element (not shown) configured to perform acombination of the various functions.

In an embodiment, feature detector 710 is configured to generate one ormore edge-based feature descriptors for digital image 750. In someembodiments, digital image 750 represents a two-dimensional (2D)representation of an object 702, as may be found in a typicalphotograph, image, or video frame. Alternatively, digital image 750 maybe a distorted image generated by utilizing atypical filters or lenses(e.g., a fish-eye lens). Moreover, digital image 750 may be a machine orrobot-view of an object based on one or more of infrared (IR) filters,X-rays, 360-degree perspective views, etc. As such, digital image 750may be one of an undistorted image, an infrared-filtered image, an x-rayimage, a 360-degree view image, a machine-view image, a frame of videodata, a graphical rendering and a perspective-view of athree-dimensional object, and may be obtained by capturing a video frameof a video stream via an image capture device, such as image capturedevice 720.

In some embodiments, image capture device 720 may be a device that iseither external (as shown) or internal to feature detector 710 forgenerating or otherwise obtaining an image of object 702. For example,image capture device 720 may comprise a remote server (e.g., aPlatform-as-a-Service (PaaS) server, an Infrastructure-as-a-Service(IaaS) server, a Software-as-a-Service (SaaS) server, or a cloud-basedserver), or a remote image database coupled to feature detector 710 viaa communications network. In another example, image capture device 720may include a digital still-image or video camera (e.g., CCD, CMOS orultrasound optical sensor) configured to capture images and/or frames ofvideo data. In another example, image capture device 720 may comprise agraphical rendering/modeling engine (e.g., a gaming system,image-rendering software, etc.) where the digital image is a generatedimage of an object rather than a captured image.

In an embodiment, feature detector 710 is configured to detect aplurality of edges 752 within digital image. For example, featuredetector 710 may detect the plurality of edges based on one of tensorvoting and a Canny edge detection algorithm. In another example, featuredetector 710 may apply one or more methods for edge detection asdescribed in U.S. patent application Ser. No. 14/623,341, entitled“Edge-Based Recognition, Systems and Methods”, filed on Feb. 16, 2015,which is incorporated in its entirety by reference herein. In someembodiments, feature detector 710 may eliminate at least one degenerateedge from the plurality of edges. Further, in some embodiments, featuredetector 710 may scale the digital image by a scaling factor, and theplurality of edges may be detected within the scaled digital image. Forexample, the scaling factor may be at least 1.5, or at least 2.0.

Feature detector 710 is further configured to select an anchor point 754located along an edge of the plurality of edges. For example, featuredetector 710 may apply a feature detection algorithm to detect aplurality of features within the digital images, and then select ananchor point from among the plurality of features determined to belocated along an edge of the plurality of edges. As such, in someembodiments, the anchor point may be a feature corresponding to at leastone of a scale-invariant feature transform (SIFT), Fast Retina Keypoint(FREAK), Histograms of Oriented Gradient (HOG), Speeded Up RobustFeatures (SURF), DAISY, Binary Robust Invariant Scalable Keypoints(BRISK), FAST, Binary Robust Independent Elementary Features (BRIEF),Harris Corners, Edges, Gradient Location and Orientation Histogram(GLOH), Energy of image Gradient (EOG) or Transform Invariant Low-rankTextures (TILT) feature. In some embodiments, the anchor point also maycomprise a detected corner of an edge or other detected inflection pointalong an edge.

In some embodiments, feature detector 710 may be further configured toselect a plurality of anchor points located along the edge, wherein theanchor points are equidistant along the edge with respect to each other.In some embodiments, the plurality of anchor points located along theedge may be selected in accordance with at least one of a determineddistribution of analysis grids along the edge, a determined amount ofanalysis grids per unit area, a determined amount of analysis grids perunit volume, a selected object model, or depth field informationassociated with the digital image.

Feature detector 710 is further configured to generate an analysis grid756, associated with the anchor point, and including a plurality ofcells. For example, the analysis grid may have a geometric center at theanchor point, and may be one of a polar grid, a radial polar grid or arectilinear grid. In some embodiments, feature detector 710 may befurther configured to orient the analysis grid based on the anchor pointnormal vector, e.g., for purposes of orientation invariance.

Feature detector 710 is further configured to calculate an anchor pointnormal vector 758 comprising a normal vector of the edge at the anchorpoint. For example, the anchor point normal vector may be one of aHarris matrix eigenvector or a geometric normal vector orthogonal to theedge at a pixel coordinate of the anchor point.

Likewise, feature detector 710 is further configured to calculate one ormore edge pixel normal vectors 760 comprising normal vectors of the edgeat one or more locations along the edge within the cells of the analysisgrid. The edge pixel normal vectors also may be one of a Harris matrixeigenvector or a geometric normal vector orthogonal to the edge at apixel coordinate.

Feature detector 710 is further configured to generate a histogram ofsimilarity 762 for each of one or more cells of the analysis grid, eachhistogram of similarity being based on a similarity measure between eachof the edge pixel normal vectors within a cell and the anchor pointnormal vector. In some embodiments, the similarity measure may be basedon one of a relative angle or a dot product between each of the edgepixel normal vectors within a cell and the anchor point normal vector.In some embodiments, the similarity measure may be based on a comparisonbetween a magnitude of each of the edge pixel normal vectors within acell and a magnitude of the anchor point normal vector. For example, themagnitude of each of the edge pixel normal vectors within a cell and themagnitude of the anchor point normal vector may be based on anon-orientation based measurement. The similarity measure also may bebased on one or more weighting factors. For example, the one or moreweighting factors may be based on one of a Euclidean distance and aGaussian weight. In some embodiments, each histogram of similarity mayinclude a plurality of bins, e.g., at least four bins or at least 16bins. Further, feature detector 710 may be further configured tonormalize bin values for the plurality of bins based on, for example, amaximum bin value (e.g., wherein the bin values are normalized to bewithin a range between 0 and 255).

Feature detector 710 is then configured to generate a descriptor 764 forthe analysis grid based on the histograms of similarity. Generating thedescriptor may include concatenating data from the histograms ofsimilarity for one or more of the cells of the analysis grid. In someembodiments, feature detector 710 may be further configured to determinea concatenation order for the data from the histograms of similarity.For example, the concatenation order may be based on an orientation ofthe cells of the analysis grid relative to the anchor point normalvector. In some embodiments, feature detector 710 may be configured tostore the descriptor in persistent storage device 730 and/or a mainmemory device 740 to, e.g., facilitate an image-based object recognitionsearch.

FIG. 8 illustrates a flow diagram of example operations for generatingan edge-based feature descriptor for a digital image in accordance withan embodiment. It should be appreciated that method 800 is executed byone or more computing devices configured to or programmed to have thedisclosed roles or responsibilities of a feature detector, such asfeature detector 710. For example, the feature detector may comprise acomputer server farm where each server is configured with, e.g., aSIFT-based image analysis package. Therefore, in some embodiments, thefeature detector may ingest millions of digital images for processingaccording method 800. Further, the feature detector may include an imagecapture device (e.g., a video camera or a gaming console) equipped tocapture image frames of video data according to method 800, such as inreal-time.

At step 802, a plurality of edges are detected within the digital image.For example, the digital image may be one of a video frame of a videostream and a rendered image. The plurality of edges may be detectedbased on one of tensor voting and a Canny edge detection algorithm.

At step 804, an anchor point located along an edge of the plurality ofedges is selected. The anchor point may be a feature corresponding to atleast one of a scale-invariant feature transform (SIFT), Fast RetinaKeypoint (FREAK), Histograms of Oriented Gradient (HOG), Speeded UpRobust Features (SURF), DAISY, Binary Robust Invariant ScalableKeypoints (BRISK), FAST, Binary Robust Independent Elementary Features(BRIEF), Harris Corners, Edges, Gradient Location and OrientationHistogram (GLOH), Energy of image Gradient (EOG) or Transform InvariantLow-rank Textures (TILT) feature.

At step 806, an analysis grid associated with the anchor point isgenerated, the analysis grid including a plurality of cells. Theanalysis grid may have a geometric center at the anchor point, and mayinclude one of a polar grid, a radial polar grid or a rectilinear grid.

An anchor point normal vector comprising a normal vector of the edge atthe anchor point is calculated at step 808. The anchor point normalvector may be one of a Harris matrix eigenvector or a geometric normalvector orthogonal to the edge at a pixel coordinate of the anchor point.

At step 810, one or more edge pixel normal vectors comprising normalvectors of the edge at one or more locations along the edge within thecells of the analysis grid are calculated. The edge pixel normal vectorsmay be one of a Harris matrix eigenvector or a geometric normal vectororthogonal to the edge at a pixel coordinate.

At step 812, a histogram of similarity is generated for each of one ormore cells of the analysis grid, each histogram of similarity beingbased on a similarity measure between each of the edge pixel normalvectors within a cell and the anchor point normal vector, and adescriptor is generated for the analysis grid based on the histograms ofsimilarity at step 814. Generating the descriptor may includeconcatenating data from the histograms of similarity for one or more ofthe cells of the analysis grid. At step 816, the descriptor may bestored, e.g., to facilitate an image-based object recognition search.

FIGS. 9-12 illustrate examples of digital images used to generateedge-based feature descriptors in accordance with an embodiment. Inparticular, FIGS. 9-12 illustrate that the embodiments herein may beutilized to generate edge-based feature descriptors that are useful forboth texture-poor and texture-rich object recognition searches.

FIG. 9 illustrates an example of generating an edge-based featuredescriptor for an image of a texture-poor object in accordance with anembodiment. In FIG. 9, digital image 900 illustrates an image of atexture-poor object (i.e., a number two). Image 910 illustrates anapplication of various embodiments herein to digital image 900. Indigital image 910, a plurality of anchor points (e.g., anchor points902) have been selected, and associated anchor point normal vectors(e.g., normal vectors 904) may be calculated for each of the anchorpoints. For example, normal vectors 904 may be Harris eigenvectors orunit normal vectors. One or more analysis grids, e.g., analysis grid906, associated with the anchor points may be generated. For example,analysis grid 906 is a radial-polar analysis grid including a pluralityof cells oriented based on the normal vector of anchor point 908. Forexample, a plurality of anchor points, and thus a plurality of analysisgrids, may be substantially evenly distributed along the edges ofdigital image 910.

Digital Images 920 and 930 illustrate anchor points that have beenselected at various scales of the original digital image 900. Forexample, digital image 900 may be scaled by a scaling factor, and aplurality of edges may be detected within the scaled digital images 920and 930. In scaled digital image 920, a plurality of anchor points(e.g., anchor points 912) have been selected, and associated anchorpoint normal vectors (e.g., normal vectors 914) may be calculated foreach of the anchor points. In scaled digital image 930, a plurality ofanchor points (e.g., anchor points 922) have been selected, andassociated anchor point normal vectors (e.g., normal vectors 924) may becalculated for each of the anchor points. As such, in an embodiment,edge-based feature descriptors may be generated for digital image 900 ata plurality of scales, e.g., to facilitate an image-based objectrecognition search. For example, edge-based feature descriptors based onanalysis grids that are evenly distributed along the edges of scaleddigital image 930 may provide a more compact set of feature descriptorsfor image 900 than, for example, a set of feature descriptors based onanalysis grids that are evenly distributed along the edges of (unscaled)digital image 910. Therefore, generating edge-based featured descriptorsfor scaled digital images may enable more compact image recognitionlibraries, e.g., an image recognition library that is practical forstorage on a mobile device.

FIG. 10 illustrates an example of image-based object recognition for animage of a texture-poor object in accordance with an embodiment. In FIG.10, edge-based feature descriptors (e.g., descriptors 1002) have beengenerated for a texture-poor image 1000 of an object, and associatednormal vectors 1004 have been calculated. For example, image 1000 may bea screen capture from a feature detection device such as, e.g., asmartphone or a tablet computer. As shown, texture-poor image 1000illustrates that the feature detection device has detected a pluralityof edges, e.g., edges 1008 and 1010. However, the object number two hasbeen recognized in texture-poor image 1000, as indicated by bounding box1006. For example, edge-based feature descriptors, e.g., descriptors1002, may be matched with stored edge-based feature descriptorsgenerated from digital image 900. As shown, the edge-based featuredescriptors generated for texture-poor image 1000 may be substantiallyevenly distributed along one or more detected edges of the image.Further, it should be noted that the edge-based feature descriptorsgenerated based on radial-polar analysis grids oriented based on anormal vector of an anchor point, e.g., normal vector 1004, have allowedfor correctly identifying the object number two within texture-poorimage 1000 despite the change in orientation of the image in relation todigital image 900. It should also be noted that the degenerate edges(e.g., edges 1010) of image 1000 have been ignored for the purposes offeature detection.

FIG. 11 illustrates an example of image-based object recognition for animage of a texture-rich object in accordance with an embodiment. FIG. 11illustrates an example of a texture-rich object 1100 that may berecognized based on edge-based feature detectors generated based on theembodiments herein. For example, the texture-rich object 1100 may be aprint ad including a plurality of features and textures, which may giverise to a plurality of edges. For example, edge-based featuredescriptors, e.g., descriptors 1102, may be recognized based on storededge-based feature descriptors generated from one or more digitalimages, as indicated by bounding box 1104. Thus, FIGS. 10 and 11illustrate that the edge-based feature descriptors disclosed herein areadaptable to resolve both texture-poor objects as well as texture-richobjects in varied surrounding environments.

FIG. 12 illustrates an example of image-based object recognition for animage of a texture-poor three-dimensional object in accordance with anembodiment. The various embodiments may also be utilized for full 3Dobjects. For example, 3D objects (e.g., an action figure toy, a vehicle,etc.) may comprise different features when viewed from differentperspectives. A video of a 3D object may be captured from differentperspectives. The frames of the video may then be treated as digitalimages. In FIG. 12, the relative edge information of the edge-basedfeature descriptors described herein may be utilized to recognizelow-texture 3D objects (in addition to 2D objects such as thoseillustrated in FIGS. 10 and 11). FIG. 12 illustrates a 3D texture-poortoy mask that includes relatively few observed features, e.g., features1202, but 3D object may be recognized based on those features asindicated by 3D bounding box 1204 established around the mask. Further,in some embodiments a relationship may be determined between one or moreof the detected edge features and a 3D structure of the object (e.g.,such as may be determined during object ingestion) to calculate thedimensions of the recognized 3D object.

Therefore, the embodiments herein may be useful to address variousefficiency, memory footprint and precision challenges associated withimage-based object recognition.

In some embodiments, the generation of edge-based feature descriptorsmay be automated. For example, feature detector 710 and/or image capturedevice 720 may operate as a web bot that crawls web sites for images toingest, e.g., images of people, social media profiles, etc. Further, thebot may operate on cityscape, streetscape or building interior images(e.g., Google® Street View images) or maps to generate edge-basedfeature descriptors associated with buildings, places or map features(e.g., a street grid pattern or topographical features). In someembodiments, feature detector 710 and/or image capture device 720 may beconfigured to generate of edge-based feature descriptors in real-time asimages or videos are captured by a web bot, or another type of automatedsystem.

Moreover, the entire infrastructure of large-scale image recognitionsystems, including the main memory and persistent storage devices,servers and user devices, can be made more efficient for processingimage recognition queries due to the various embodiments.

Systems, apparatus, and methods described herein may be implementedusing digital circuitry, or using one or more computers using well-knowncomputer processors, memory units, storage devices, computer software,and other components. Typically, a computer includes a processor forexecuting instructions and one or more memories for storing instructionsand data. A computer may also include, or be coupled to, one or moremass storage devices, such as one or more magnetic disks, internal harddisks and removable disks, magneto-optical disks, optical disks, etc.

Systems, apparatus, and methods described herein may be implementedusing a computer program product tangibly embodied in an informationcarrier, e.g., in a non-transitory machine-readable storage device, forexecution by a programmable processor; and the method steps describedherein, including one or more of the steps of FIG. 8, may be implementedusing one or more computer programs that are executable by such aprocessor. A computer program is a set of computer program instructionsthat can be used, directly or indirectly, in a computer to perform acertain activity or bring about a certain result. A computer program canbe written in any form of programming language, including compiled orinterpreted languages, and it can be deployed in any form, including asa stand-alone program or as a module, component, subroutine, or otherunit suitable for use in a computing environment.

A high-level block diagram of an exemplary apparatus that may be used toimplement systems, apparatus and methods described herein is illustratedin FIG. 13. Apparatus 1300 comprises a processor 1310 operativelycoupled to a persistent storage device 1320 and a main memory device1330. Processor 1310 controls the overall operation of apparatus 1300 byexecuting computer program instructions that define such operations. Thecomputer program instructions may be stored in persistent storage device1320, or other computer-readable medium, and loaded into main memorydevice 1330 when execution of the computer program instructions isdesired. For example, feature detector 710 and image capture device 720may comprise one or more components of computer 1300. Thus, the methodsteps of FIG. 8 can be defined by the computer program instructionsstored in main memory device 1330 and/or persistent storage device 1320and controlled by processor 1310 executing the computer programinstructions. For example, the computer program instructions can beimplemented as computer executable code programmed by one skilled in theart to perform an algorithm defined by the method steps of FIG. 8.Accordingly, by executing the computer program instructions, theprocessor 1310 executes an algorithm defined by the method steps of FIG.8. Apparatus 1300 also includes one or more network interfaces 1380 forcommunicating with other devices via a network. Apparatus 1300 may alsoinclude one or more input/output devices 1390 that enable userinteraction with apparatus 1300 (e.g., display, keyboard, mouse,speakers, buttons, etc.).

Processor 1310 may include both general and special purposemicroprocessors, and may be the sole processor or one of multipleprocessors of apparatus 1300. Processor 1310 may comprise one or morecentral processing units (CPUs), for example. Processor 1310, persistentstorage device 1320, and/or main memory device 1330 may include, besupplemented by, or incorporated in, one or more application-specificintegrated circuits (ASICs) and/or one or more field programmable gatearrays (FPGAs).

Persistent storage device 1320 and main memory device 1330 each comprisea tangible non-transitory computer readable storage medium. Persistentstorage device 1320, and main memory device 1330, may each includehigh-speed random access memory, such as dynamic random access memory(DRAM), static random access memory (SRAM), double data rate synchronousdynamic random access memory (DDR RAM), or other random access solidstate memory devices, and may include non-volatile memory, such as oneor more magnetic disk storage devices such as internal hard disks andremovable disks, magneto-optical disk storage devices, optical diskstorage devices, flash memory devices, semiconductor memory devices,such as erasable programmable read-only memory (EPROM), electricallyerasable programmable read-only memory (EEPROM), compact disc read-onlymemory (CD-ROM), digital versatile disc read-only memory (DVD-ROM)disks, or other non-volatile solid state storage devices.

Input/output devices 1390 may include peripherals, such as a printer,scanner, display screen, etc. For example, input/output devices 1390 mayinclude a display device such as a cathode ray tube (CRT), plasma orliquid crystal display (LCD) monitor for displaying information (e.g., aplurality of image transformations for selection) to a user, a keyboard,and a pointing device such as a mouse or a trackball by which the usercan provide input to apparatus 1300.

Any or all of the systems and apparatus discussed herein, includingfeature detector 710 and image capture device 720 may be performed by,and/or incorporated in, an apparatus such as apparatus 1300.

One skilled in the art will recognize that an implementation of anactual computer or computer system may have other structures and maycontain other components as well, and that FIG. 13 is a high levelrepresentation of some of the components of such a computer forillustrative purposes.

The foregoing specification is to be understood as being in everyrespect illustrative and exemplary, but not restrictive, and the scopeof the invention disclosed herein is not to be determined from thespecification, but rather from the claims as interpreted according tothe full breadth permitted by the patent laws. It is to be understoodthat the embodiments shown and described herein are only illustrative ofthe principles of the present invention and that various modificationsmay be implemented by those skilled in the art without departing fromthe scope and spirit of the invention. Those skilled in the art couldimplement various other feature combinations without departing from thescope and spirit of the invention.

What is claimed is:
 1. A method of generating an edge-based featuredescriptor for a digital image at a feature detection device, the methodcomprising: detecting, by the feature detection device, a plurality ofedges within the digital image; selecting, by the feature detectiondevice, an anchor point located along an edge of the plurality of edges;generating, by the feature detection device, an analysis grid associatedwith the anchor point, the analysis grid including a plurality of cells;calculating, by the feature detection device, an anchor point normalvector comprising a normal vector of the edge at the anchor point;calculating, by the feature detection device, one or more edge pixelnormal vectors comprising normal vectors of the edge at one or morelocations along the edge within the cells of the analysis grid;generating, by the feature detection device, a histogram of similarityfor each of one or more cells of the analysis grid, each histogram ofsimilarity being based on a similarity measure between each of the edgepixel normal vectors within a cell and the anchor point normal vector;and generating, by the feature detection device, a descriptor for theanalysis grid based on the histograms of similarity.
 2. The method ofclaim 1, wherein the digital image is one of a video frame of a videostream and a rendered image.
 3. The method of claim 1, wherein theplurality of edges is detected based on one of tensor voting and a Cannyedge detection algorithm.
 4. The method of claim 1, further comprisingeliminating at least one degenerate edge from the plurality of edges. 5.The method of claim 1, further comprising: scaling the digital image bya scaling factor; and detecting the plurality of edges within the scaleddigital image.
 6. The method of claim 5, wherein the scaling factor isat least 1.5.
 7. The method of claim 5, wherein the scaling factor is atleast 2.0.
 8. The method of claim 1, wherein the anchor point is afeature corresponding to at least one of a scale-invariant featuretransform (SIFT), Fast Retina Keypoint (FREAK), Histograms of OrientedGradient (HOG), Speeded Up Robust Features (SURF), DAISY, Binary RobustInvariant Scalable Keypoints (BRISK), FAST, Binary Robust IndependentElementary Features (BRIEF), Harris Corners, Edges, Gradient Locationand Orientation Histogram (GLOH), Energy of image Gradient (EOG) orTransform Invariant Low-rank Textures (TILT) feature.
 9. The method ofclaim 1, wherein the anchor point comprises a detected corner of theedge.
 10. The method of claim 1, wherein the analysis grid has ageometric center at the anchor point.
 11. The method of claim 1, whereinthe analysis grid includes one of a polar grid, a radial polar grid or arectilinear grid.
 12. The method of claim 11, wherein the analysis gridis oriented based on the anchor point normal vector.
 13. The method ofclaim 1, wherein the analysis grid comprises at least five cells. 14.The method of claim 1, wherein the analysis grid comprises at least ninecells.
 15. The method of claim 1, wherein the anchor point normal vectoris one of a Harris matrix eigenvector or a geometric normal vectororthogonal to the edge at a pixel coordinate of the anchor point. 16.The method of claim 1, wherein each of the edge pixel normal vectors isone of a Harris matrix eigenvector or a geometric normal vectororthogonal to the edge at a pixel coordinate.
 17. The method of claim 1,wherein the similarity measure is based on one of a relative angle or adot product between each of the edge pixel normal vectors within a celland the anchor point normal vector.
 18. The method of claim 1, whereinthe similarity measure is based on a comparison between a magnitude ofeach of the edge pixel normal vectors within a cell and a magnitude ofthe anchor point normal vector.
 19. The method of claim 18, wherein themagnitude of each of the edge pixel normal vectors within a cell and themagnitude of the anchor point normal vector are based on anon-orientation based measurement.
 20. The method of claim 1, whereinthe similarity measure is based on one or more weighting factors. 21.The method of claim 20, wherein the one or more weighting factors arebased on one of a Euclidean distance and a Gaussian weight.
 22. Themethod of claim 1, wherein each histogram of similarity includes aplurality of bins.
 23. The method of claim 22, wherein each histogram ofsimilarity includes at least four bins.
 24. The method of claim 22,wherein each histogram of similarity includes at least 16 bins.
 25. Themethod of claim 22, wherein bin values for the plurality of bins arenormalized based on a maximum bin value.
 26. The method of claim 25,wherein bin values for the plurality of bins range between 0 and 255.27. The method of claim 1, wherein generating the descriptor includesconcatenating data from the histograms of similarity for one or more ofthe cells of the analysis grid.
 28. The method of claim 27, furthercomprising determining a concatenation order for the data from thehistograms of similarity.
 29. The method of claim 28, wherein theconcatenation order is based on an orientation of the cells of theanalysis grid relative to the anchor point normal vector.
 30. The methodof claim 1, wherein the descriptor is a multi-dimensional vector havinga number of dimensions based on a number of cells in the analysis grid.31. The method of claim 1, wherein the descriptor is a multi-dimensionalvector having a number of dimensions based on a total number of bins inthe histograms of similarity for the analysis grid.
 32. The method ofclaim 1, further comprising selecting a plurality of anchor pointslocated along the edge, wherein the anchor points are equidistant alongthe edge with respect to each other.
 33. The method of claim 1, furthercomprising selecting a plurality of anchor points located along the edgein accordance with at least one of a determined distribution of analysisgrids along the edge, a determined amount of analysis grids per unitarea, a determined amount of analysis grids per unit volume, a selectedobject model, or depth field information associated with the digitalimage.
 34. The method of claim 1, further comprising facilitating animage-based object recognition search using the descriptor for theanalysis grid.
 35. A system for generating an edge-based featuredescriptor for a digital image, the system comprising: a processor; amemory device; and a feature detector executable on the processoraccording to software instructions stored in the memory device, thefeature detector being configured to: detect a plurality of edges withinthe digital image; select an anchor point located along an edge of theplurality of edges; generate an analysis grid associated with the anchorpoint, the analysis grid including a plurality of cells; calculate ananchor point normal vector comprising a normal vector of the edge at theanchor point; calculate one or more edge pixel normal vectors comprisingnormal vectors of the edge at one or more locations along the edgewithin the cells of the analysis grid; generate a histogram ofsimilarity for each of one or more cells of the analysis grid, eachhistogram of similarity being based on a similarity measure between eachof the edge pixel normal vectors within a cell and the anchor pointnormal vector; and generate a descriptor for the analysis grid based onthe histograms of similarity.
 36. A computer program product embedded ina non-transitory computer readable medium comprising instructionsexecutable by a computer processor to generate an edge-based featuredescriptor for a digital image, the instructions being executable by acomputer processor to execute processing comprising: detecting aplurality of edges within the digital image; selecting an anchor pointlocated along an edge of the plurality of edges; generating an analysisgrid associated with the anchor point, the analysis grid including aplurality of cells; calculating an anchor point normal vector comprisinga normal vector of the edge at the anchor point; calculating one or moreedge pixel normal vectors comprising normal vectors of the edge at oneor more locations along the edge within the cells of the analysis grid;generating a histogram of similarity for each of one or more cells ofthe analysis grid, each histogram of similarity being based on asimilarity measure between each of the edge pixel normal vectors withina cell and the anchor point normal vector; and generating a descriptorfor the analysis grid based on the histograms of similarity.